The evolutionary emergence of each facet of human language can be viewed as a 'transition'. This book explores how different transitions took place, their preconditions, and their consequences. Among the questions it addresses are: what physiological and psychological differences between us and other animals lie at the heart of our superior capacity for language? Was the pre-linguistic period of humankind characterized by words without syntax, syntax without meaning, gesture without speech, or all, or none, of these? Once a community is ready and able to develop language, what internal and external factors trigger its emergence? How are we to interpret the archaeological evidence of early tool-making abilities, relative to the presence, or absence, of language? In what social circumstances could language have avoided being immediately harnessed for deception, so that it became too dangerous and unreliable to be of value? Was the universal form of language determined by pre-existing psychological capabilities, or by natural constraints in communication? Has language finished evolving? If not, how different were linguistic structures used by our early ancestors from those that we use today? This investigation into one of the enduring mysteries of humankind brings together original contributions from linguists, archaeologists, anthropologists, psychologists, biologists, primatologists, and researchers in artificial intelligence. They offer the reader up-to-the-minute debates in the field of language evolution.